PROJECT SUMMARY/ABSTRACT This proposal, ?Use and Impact of Dietary Supplements in Heart Failure (HF)? is in response to PA-17-307, Administrative Supplement for Research on Dietary Supplements and leverages the recently NHLBI-funded RO1 (R01HL136407-01), which applies a cluster randomized trial to assess the effects of the Heart Exercise And Resistance Training ? Peer Lead ActivitY (HEART?PLAY) intervention in a community dwelling sample of people with Heart Failure (HF), in order to administer a detailed survey of their use of dietary supplements. In order to maximize sample size in cross-sectional analyses, the proposed research will survey all candidate participants (n?350) for their supplement use (including types, dosages and frequency) during their Screening interviews, and will administer a validated health-related quality of life questionnaire (PROMIS- 29), to determine if use of specific dietary supplements is associated with differences in QOL, including functional symptoms like sleep, pain and energy, and/or clinical status (adjusted for type of HF, age, sex and time since diagnosis) (Aim1). Additionally, we will perform a more detailed assessment of supplement use, in the context of diet, in all enrolled participants (n=200) in HEART-PLAY, by administering a validated food frequency questionnaire to determine dietary intake of individual nutrients, as well as, measure biomarkers of three specific nutrients that have mixed evidence in HF, i.e., omega-3 fatty acids (?-3), vitamin D (VitD) and coenzyme Q10 (CoQ10). By collecting this detailed information on supplement use, dietary intake and physiologic status of three target nutrients, we will determine if use of ?-3, VitD, and/or CoQ10 supplements is associated differences in physiologic status for each nutrient, adjusted for age, sex, type of HF, and dietary intake (Aim 2). We will also determine if use of supplements is associated with differences in functional symptoms and/or clinical severity in people with HF, adjusted for age, sex, CHF type (HFpEF or HFrEF), clinical stage, dietary intake, and time since diagnosis (Aim 3). The proposed research contributes to research gaps related to unknown effects of ?-3, VitD, and CoQ10 in HF, by also considering dietary intake, and applying specific biomarkers to objectify physiologic status for each nutrient. The results of this research will inform the selection of outcome measures, and potentially interventions, for future clinical trials of community- dwelling adults with HF.